High impedance circuit for injection locked magnetrons

ABSTRACT

A high impedance circuit has radially disposed first vanes and radially disposed second vanes interdigitating between the first vanes. The first vanes and the second vanes are each interconnected by a first toroidal strap and a second toroidal strap, respectively. The first strap and the second strap are disposed co-axially on opposite sides of the vane structure. The vanes and straps are dimensioned so that the circuit has a single cavity impedance commensurate with a predetermined interaction impedance for the oscillator which is sufficient to sustain oscillation for a preselected injection locking band-width of the oscillator.

FIELD OF INVENTION

The present invention relates generally to injection locked magnetronsand more particularly to a high impedance circuit utilizing a novel vanestructure.

BACKGROUND OF THE INVENTION

A study of injection locking of non-coherent oscillators is described inAdler, "A Study of Locking Phenomenon in Oscillators,". Proceedings ofthe IRE, June, 1946, pages 351-357. As described therein, the coherentbandwidth, ΔF, of an injection locked oscillator is substantially equalto the ratio given by (1) the product of twice the frequency of theoscillator and the square root of the ratio of the injected coherentpower to the output power of the oscillator to (2) the external Q of theoscillator.

The study of injection locking by Adler was further developed by others.For example, see Huntoon & Weiss, "Synchronization of Oscillators,"Proceedings of the IRE, December, 1947, pages 1415-1423. The Huntoonreference provides a strong theoretical basis for injection lockingregardless of circuit configuration.

One of the earlier articles relating to the injection locking ofmagnetron oscillators is given in David, "R. F. Phase Control and PulsedMagnetrons," Proceedings of the IRE, June, 1952, pages 669-685. Althoughthe theoretical concept of injection locking of magnetrons is known, thepractical reduction to practice in the prior art of injection lockedmagnetrons has not been realized until relatively recently. First,Appropriate low cost coherent sources of RF energy with sufficient powerto drive magnetrons have not been available. Secondly, the existingmagnetron circuits have an apparent limitation which limit theobtainable circuit bandwidth. The disadvantage resulting from thislimitation is that the known magnetron circuits were insufficient forcommercial exploitation.

Recent advances in solid state oscillators have all but eliminated thefirst limitation of the prior art noted above. Power levels formagnetrons are now .[.aVailable.]. .Iadd.available .Iaddend.in the 0.5to 5.0 kilowatt level. With current devices, coherent gains of ten tothirteen dB are achievable over narrow bandwidths. The exploitation ofthese advances for magnetrons has, however, been limited by the abilityof conventional magnetron circuits to present a sufficiently highimpedance to the electron stream in the interaction region to sustainproper magnetron operation over a sufficiently wide bandwidth.

In a known prior art magnetron with a conventional circuitconfiguration, manipulation of the coupling between the conventionalcircuit and its external load will reduce its external Q. The reductionof the external Q will achieve a wider injection locking bandwidth.Because of the fundamental relationship between the external Q and theloaded Q, this will cause the fields on the magnetron circuit to becomelower and lower until a phenomenon called "sink" is reached. At thispoint the magnetron ceases to work. The reason is that the total RFimpedance of the circuit becomes too low to sustain oscillation.

The fundamental relationships which govern this sink phenomenon can besummarized as follows:

    ΔF=2F.sub.o (P.sub.i /P.sub.o).sup.1/2 /Q.sub.e

    Z.sub.int =Q.sub.l (L/C).sup.1/2

    1/Q.sub.l =1/Q.sub.o +1/Q.sub.e

wherein the locking bandwidth ΔF is given by Adler's equation, Z_(int)is the interaction impedance of the magnetron, Q_(o) is the unloaded Qof the magnetron circuit and is a function of the frequency of themagnetron, Q_(l) is the loaded Q of the circuit, Q_(e) is the external Qof the circuit, and .[.(L/C)¹⁷⁸ .]. (.Iadd.L/C)^(1/2) .Iaddend. is thesingle cavity impedance of the magnetron and is a function of theconfiguration of the circuit.

From the above equations, it can be seen that the interaction impedanceis the product of the loaded Q, Q_(l), and the single cavity impedanceof the magnetron. Because of the fundamental relationship between theloaded Q, which is related to the ability to maintain oscillation, andthe external Q, which is related to the ability to obtain largeinjection bandwidth, decreasing the external Q for a fixed circuitdecreases the loaded Q. As a consequence thereof, the interactionimpedance Z_(int), is also decreased.

SUMMARY OF THE INVENTION

The present invention is directed to a novel high impedance circuit tosatisfy the conflicting requirements of wide bandwidth and sufficientcircuit impedance so as to increase the single cavity impedance of themagnetron. The novel circuit, in lumped constant terms is a very highinductive, very low capacitive circuit.

According to the present invention, the high impedance circuit hasradially disposed first vanes and radially disposed second vanesinterdigitating between the first vanes. The first vanes and the secondvanes are each interconnected by a first toroidal strap and a secondtoroidal strap, respectively. The first strap and the second strap aredisposed co-axially on opposite sides of the vane structure. The vanesand straps are dimensioned so that the circuit has a single cavityimpedance commensurate with a predetermined interaction impedance forthe oscillator which is sufficient to sustain oscillation for apreselected injection locking bandwidth of the oscillator, in accordancewith the above equations.

In one embodiment of the present invention, each of the vanes isgenerally T-shaped. Each vane has a relatively wide high conductivefirst portion and a relatively high inductance second portion. The firstportion is disposed proximate to an axis of the cavity with the secondportion extending radially outward therefrom.

Advantages of the present invention are the high-single cavity impedanceof greater than 200 ohms in a 16 resonator configuration and a wide vaneface which presents an adequate peak dissipation surface to the electronstream of the interaction space. This is an especially importantadvantage for high power applications. Other advantages of the presentinvention allow the independent control of the interaction impedance andthe external Q by divorcing the single cavity impedance from thecoupling circuit which controls the band-width. The simple shape of thevane allows it to be fabricated using conventional stamping operations.The toroidal strap can be easily made from available wire through asimple forming operation. The designs facilitate the manufacture of thecircuit thereby reducing its cost.

These and other objects, advantages and features of the presentinvention will be readily apparent to those skilled in the art from astudy of the following description of an exemplary preferred embodimentwhen read in conjunction with the attached drawings and appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of a typical magnetron oscillator circuitused in the prior art;

FIG. 2 is one view of the novel high impedance circuit constructed inaccordance with the principles of the present invention;

FIG. 3 is a view taken along line 3--3 of FIG. 2; and

FIG. 4 is an enlarged view of a portion of FIG. 3.

DESCRIPTION OF AN EXEMPLARY PREFERRED EMBODIMENT

Referring now to FIG. 1, there is shown a schematic diagram illustratingthe use of an injection lock magnetron 10. The source 12 of coherentmicrowave energy delivers low power energy to a circulator 14. Thecirculator injects the lower power energy into the magnetron 10. The lowpower energy is amplified by the magnetron 10 as is well known in theart. The amplified energy developed by the magnetron 10 is redirected tothe circulator 14. The high power microwave energy is then coupled to anantenna 16 to radiate the high power coherent output energy.

Referring now to FIGS. 2-4, there is shown a high, impedance circuit 20for an anode ring 22 in the magnetron 20. As is well known in the art,the circuit 20 is disposed within an inner cavity 24 of the anode ring22.

The high impedance circuit 20 includes a plurality of first radial vanes26¹ and a plurality of second radial vanes 26². The first radial vanes26¹ are coaxially positionable within the cavity 24. The second radialvanes 26² are interdigital with the first vanes 26¹ to form a vanestructure 28. Each of the first vanes 26¹ and second vanes 26² has arelatively wide high conductance first portion 30 and a relativelynarrow high inductance portion 32, as best seen in FIG. 4. The secondportion 32 extends radially outward from the first portion 30. The firstportion 30 is radially proximate to an axis 34 of the cavity about whichthe magnetron cathode is disposed.

The circuit further includes a first toroidal strap 26 and a secondtoroidal strap 38. Each of the first strap 36 and the second strap 38are coaxial with the axis 34. The first strap is disposed along thefirst side of the vane structure 28. The second strap is disposed alongthe second side of the vane structure 28. The first strap interconnectsthe first vanes 26¹ and the second strap 38 interconnects the secondvanes 26².

According to the present invention, each of the vanes 26¹, 26², thefirst strap 36, and second strap 38 are dimensioned so that the circuit20 has a single cavity impedance commensurate with a predeterminedinteraction impedance of the oscillator which is sufficient to sustainoscillation for a preselected injection locking bandwidth, as is derivedfrom the above references. More particularly, the relatively narrowsecond portion 32 concentrates rings of magnetic field, B, around thevane 26, as best seen in FIG. 4, to create a high inductance. Theelectric field between the vanes reverses direction between each of thefirst vanes 26¹ and the second vanes 26². The straps, being of circularcross-section, minimize capacitance of the circuit, while givingsufficient mode separation. Where the straps 36, 38 are connected to theappropriate one of the vanes 26¹, 26², a mounting portion 40 is providedtherein with an annular channel 42. The second portion 32 of the vanesmay be soldered to the anode ring 22.

By the equations given above, for a given injection lock bandwidth, ΔF,the interactive impedance, Z_(int), can be selected so that oscillationis maintained. It has been found that the interactive impedance, in thepreferred embodiment, should be at least 5000 ohms. The shape of thevanes 26 are then structured so their inductance and capacitancesatisfies the conditions set forth in the above equations. The T-shapeof the vanes 26¹, 26², has been found to satisfy these conditions.

There has been described hereinabove a novel high impedance circuit foruse in the anode ring of a magnetron. It is obvious that those skilledin the art may make numerous uses of the departures from the preferredembodiment of the present invention without departing from the inventiveconcepts herein. Accordingly, the present invention is to be definedsolely by the scope of the following claims.

What is claimed is:
 1. A high impedance circuit for an anode ring in aninjection locked oscillator, said anode ring having an inner cavity,said circuit comprising:a plurality of first radial vanes coaxiallypositionable in said cavity; a plurality of second radial vanesinterdigitating with said first vanes to form a vane structure; saidfirst and second vanes each having a relatively narrow high inductanceportion; a first toroidal strap coaxially disposed along a .[.first.].side of said vane structure, said first strap interconnecting said firstvanes; a second toroidal strap coaxially disposed along .[.the second.]..Iadd.a .Iaddend.side of said vane structure, said second strapinterconnecting said second vanes; said first and second straps eachhaving a relatively low capacitance due to said toroidal shape; and saidfirst vanes, said second vanes, said first strap, and said second strapbeing dimensioned so that said circuit has a high single cavityimpedance commensurate with an interaction impedance of said oscillatorwhich is sufficient to sustain oscillation for a preselected injectionlocking bandwidth of said oscillator.
 2. A circuit as set forth in claim1, wherein: said injection locking bandwidth, ΔF, is given by:

    ΔF=2F.sub.o (P.sub.i /P.sub.o).[..sup.178 .]. .Iadd..sup.1/2.Iaddend. /Q.sub.e

wherein F_(o) is the frequency of said oscillator, P_(o) is the powerout of said oscillator, P_(i) is the injected coherent power, and Q_(e)is the external Q of said oscillator; further wherein: said interactionimpedance, Z_(int), is given by:

    Z.sub.int =Q.sub.l (L/C).sup.1/2

wherein Q_(l) is the loaded Q of said circuit, and (L/C).[.¹⁷⁸ .]..Iadd.^(1/2) .Iaddend. is said high single cavity impedance of saidcircuit; and further wherein: said loaded Q, Q_(l), is given by:

    1/Q.sub.l =1/Q.sub.o +1/Q.sub.e

wherein Q_(o) is the unloaded Q of said circuit.
 3. The circuit as setforth in claim 2, wherein said interactive impedance is at least 5000ohms.
 4. A circuit as set forth in claim 1, wherein each of said firstvanes and said second vanes are identically configured, having arelatively wide .[.high conductance.]. first portion radially proximateto an axis of said cavity and a second portion formed by said relativelynarrow high inductance portion extending radially outward from saidfirst portion where said narrow second portion connects said first andsecond vanes to said anode ring.
 5. A circuit as set forth in claim 1,wherein said first vanes and said second vanes are T-shaped.
 6. Acircuit as set forth in claim 5, wherein:said first T-shaped vanes havea mounting portion between the top of said T-shape and one side of saidnarrow portion of said T-shape for connecting said first toroidal strapthereto; said second T-shaped vanes have a mounting portion between thetop of said T-shape and the opposite side of said narrow portion of saidT-shape for connecting said second toroidal strap thereto; and saidfirst vanes and said second vanes are identically shaped and oppositelydisposed within said anode ring.
 7. A high impedance circuit for ananode ring in an injection locked magnetron, comprising:a plurality ofvanes each having a narrow portion .[.for increasing the inductance ofsaid circuit.]..Iadd., said circuit having an increased inductance dueto said narrow portion.Iaddend.; at least one strap having a toroidalshape .[.including a circular cross-section for decreasing thecapacitance of said circuit.]..Iadd., said circuit having a decreasedcapacitance due to said toroidal shape.Iaddend.; wherein the combinationof said increased inductance and decreased capacitance increases theimpedance of said circuit.
 8. A circuit as set forth in claim 7,wherein:said plurality of vanes are T-shaped.
 9. A circuit as set forthin claim 8, wherein:said plurality of T-shaped vanes each include anannular channel between the top of said T-shaped vane and said narrowportion thereof; said vanes are mounted within said circuit with saidchannel up and, alternately, with said channel down; and said at leastone strap includes two straps, a first strap for electrical connectionto said plurality of vanes with said channel in said up mounted positionand a second strap for electrical connection to said plurality of vaneswith said channel in said down mounted position. .Iadd.
 10. A highimpedance circuit for an injection locked oscillator having an innercavity, said circuit comprising:a plurality of vanes coaxiallypositionable in said cavity; and at least one strap interconnecting aportion of said vanes, said vanes and strap being dimensioned so thatsaid circuit has a high single cavity impedance commensurate with aninteraction impedance of said oscillator which is sufficient to sustainoscillation for a preselected injection locking bandwidth of saidoscillator; wherein said injection locking bandwidth, ΔF, is given by:##EQU1## wherein F_(o) is the frequency of said oscillator, P_(o) ispower out of said oscillator, P_(i) is the injected coherent power, andQ_(e) is the external Q of said oscillator; further wherein saidinteraction impedance, Z_(int), is given by: ##EQU2## wherein Q_(l) isthe loaded Q of said circuit, and (L/C)^(1/2) is said high single cavityimpedance of said circuit; and further wherein Q_(l) is given by:##EQU3## wherein Q_(o) is the unloaded Q of the circuit and saidinteraction impedance is at least 5,000 ohms. .Iaddend. .Iadd.
 11. Acircuit as set forth in claim 10, wherein said plurality of vanes aregenerally T-shaped. .Iaddend. .Iadd.12. A circuit as set forth in claim10, wherein said plurality of vanes includes first vanes interdigitallydisposed in said cavity with second vanes. .Iaddend. .Iadd.13. A circuitas set forth in claim 12, wherein each of said first vanes and saidsecond vanes are identically configured, having a relatively wide firstportion radially proximate to an axis of said cavity and a relativelynarrow high inductance second portion extending radially outward fromsaid first portion where said narrow second portion connects said firstand second vanes to said circuit. .Iaddend. .Iadd.14. A circuit as setforth in claim 13, wherein said at least one strap includes two straps,a first strap electrically connecting said first vanes and a secondstrap electrically connecting said second vanes. .Iaddend. .Iadd. Acircuit as set forth in claim 14, wherein said straps have a toroidalshape including a circular cross-section providing decreased capacitanceof said circuit. .Iaddend. .Iadd.16. A circuit as set forth in claim 14,wherein said first vanes have a first mounting portion on a first sidebetween said wide portion and said narrow portion, said first strapbeing connected to said first vanes at said first mounting portion..Iaddend. .Iadd.17. A circuit as set forth in claim 16, wherein saidsecond vanes have a second mounting portion on a second side betweensaid wide portion and said narrow portion, said second strap beingconnected to said second vanes at said second mounting portion..Iaddend. .Iadd.18. A circuit as set forth in claim 12, wherein saidfirst vanes and said second vanes are oppositely disposed within saidcircuit. .Iaddend. .Iadd.19. A circuit as set forth in claim 10, furthercomprising an anode ring providing said cavity. .Iaddend. .Iadd.20. Acircuit as set forth in claim 10, wherein said oscillator is amagnetron. .Iaddend.